Biodiversity is the variety of living organisms. There are different biological levels of biodiversity: from the very small differences linked to the genetic variances within the same species to different species, genus, different families until the highest taxonomic groups.

Biodiversity is normally divided into three levels: genetic variation, species variation and variety of ecosystem. Of these the most commonly used is the variety of species as a synonym for the richness of species. The variety of species is the number of species present in a particular site or habitat.

Without any doubt the richest environment in number of species is the tropical rain forest. Despite this environment occupying only 7% of the surface of the Earth, it provides a home to more than half of all living species.

The decline of biodiversity
The decline of biodiversity takes various forms but inevitably leads to the extinction of species. From a geological point of view every species has a life-cycle.

The extinction of species is, in a certain way, therefore a natural phenomenon. In the last 600 million years the trend of biodiversity has always been towards growth, despite the occurrence of five mass extinctions of which the most famous is that of the dinosaurs which happened at the end of Cretaceous period 65 million years ago.

It is more and more evident that, in the last decades, we are contributing to the sixth mass extinction, this time caused, directly or indirectly, by man. The difference between this and the previous ones is that the rate of extinction is incredibly faster than that the past.

About 27,000 species of plants and animals are made extinct every year by the activity of man i.e. 74 species a day, three an hour. Before man interfered with the environment, species survived for a period in the realm millions of years (as evident from fossil documentation) which means that the normal basic rate of extinction is 1 species a year for every million species which exist. Human activity has increased the rate of extinction by between 1000 and 10.000 times. Therefore we find ourselves in the middle of one of the strongest waves of extinction that has ever happen on the Earth.

The causes of the extinction of species due to man, can be divided into two categories:

direct (hunting and excessive captivity and introduction of alien species)

indirect (the destruction and modification of habitat)

Excessive hunting is maybe the most obvious cause of extinction but, in global terms, its contribution to the loss of biodiversity is undoubtedly less important than the indirect causes. Virtually every type of human activity leads to the modification of the natural environment. In particular the reduction and destruction of entire ecosystem, the fragmentation of environments into small, non-self sufficient parts and pollution and contaminants in the natural environments, all influence the relative number of species. In extreme cases these can cause extinction.

Why Conserve Biodiversity
Biodiversity is our most precious resource but we don't always manage to appreciate its value.The reasons to conserve biodiversity are numerous and important.

The biodiversity is a biological resource and maintains favorable conditions in the biosphere for human life, in particular as a food source and medicine for humanity. About 80% of the population of developing countries use medicines taken from natural substances despite the relative unavailability of medical products in the west. Actually about 120 substances extracted from 90 species of plants are used in medicine. It is known that the synthetic derivatives are less efficient therapeutically then natural products. The species used are only a very small part of those potentially useable, one of the main worries of researchers is that the reduction of biodiversity could prevent the use of these substances that, in the future, could cure important illnesses.

Other functions of biodiversity include the role of forests in the regulation of water basins and the stabilization of soil, preventing erosion; the role of mangroves in the stabilization of tropical coastal areas and the reproduction of fish; the role of coral reefs in the survival of innumerable species; the role that protective areas have in the economy of many developing countries trough the income of eco tourism.

In every case the conservation of biodiversity doesn't have to be justified only by economic advantages but also for moral and aesthetic values. There are two types of reasons:

“precautionary” - there are species which don't actually have an apparent value but which could have in the future.

“future generation” - we have to leave the maximum amount of biodiversity to our future generation. The conservation of biodiversity is the duty of every singular human being, who must have the awareness that the effects of daily actions can produce enormous results. Only this will change the tragic decline of nature that characterizes this period of history.